Portland's Big Pipe

Staff | September 28, 2010

The East Side Combined Sewer Outflow project in Portland is designed to significantly reduce the city's sewage and storm water overflows into the Willamette River. When completed in December 2011, it will collect and intercept overflows from 12 existing combined sewer outfalls that discharge to the river.

Main contractor KBB, a joint venture led by Kiewit Construction with Bilfinger+Berger, is constructing a 22-foot-diameter tunnel that runs for six miles along the east bank of the Willamette River in Portland and connects to a similar project on the west side at the Swan Island Pump Station. At $382.5 million, the East Side CSO — known locally as The Big Pipe — is the largest public works contract ever let by the city of Portland.

The tunnel route begins at SE 17th and McLoughlin Boulevard and will end on Swan Island, where it will be connected to the Confluent Shaft. The tunnel boring machine — nicknamed "Rosie" — started boring in May 2007 from the Opera Shaft, moving north towards the Port Center Shaft at the Swan Island Pump Station. From there, the TBM will be removed and transported back to the Opera Shaft to tunnel south towards the McLoughlin Shaft.

The Confluent Shaft connects to the Swan Island Pump Station. The pump station will pump sewage through the Portsmouth Force Main, a pressurized pipe Environmental Services will build as one of the East Side CSO projects. The force main will discharge to an existing tunnel, which will take the flow to the Columbia Boulevard Wastewater Treatment Plant.

Seven shafts, ranging from 49 feet to 67 feet in diameter and ranging from 120 feet to 160 feet deep, are being built along the route of the tunnel. Construction on these began in March 2006, paving the way for tunnel boring to begin. As of mid-November 2008, six of the seven shafts had been completed.

The shafts are being formed by constructing a slurry wall and then excavating within. Excavation is carried out using a Liebherr HS 895 HD duty-cycle crawler crane fitted with clamshell bucket. Periodically a drop chisel was required to loosen highly consolidated sand/silt/gravel formations.

On completion of an excavation, the crane also is used to support the construction and installation of rebar mats, as well as tremie concrete operations, before moving on to the next shaft excavation operation.

The HS 895 HD is the largest model in Liebherr's series of duty cycle cranes. It has a maximum rated lifting capacity of 220 tons and has a maximum main boom length of 276 feet. Maximum boom length when fitted with clamshell or dragline is 181 feet. The 12-cylinder MAN diesel engine generates 900 horsepower at 1,900 rpm.

Clutch and braking functions on the free fall system are provided by a compact designed, low wear and maintenance-free multidisc brake. The drag and hoist winches use pressure-controlled, variable flow hydraulic motors, with sensors that automatically adjust oil flow to provide max winch speed depending on the load. The winch can produce a line pull of 66,200 pounds.

Pipeline Work

The city of Portland issued a project update on Jan. 28. At Outfall 28 (SE Insley Street and 18th Avenue) the microtunnel boring machine was retrieved on Dec. 31. The 84-inch pipeline from the McLoughlin Shaft to this location is complete. The next phase of work includes the buildout of the shaft, installation of a 144-inch manhole structure, shaft backfilling, installation of permanent sewer and water pipelines, curbs and sidewalk replacement, and street paving. The street and intersection will remain closed until mid-April while this work continues.

The updated schedule for the completion of Outfall 36 (SE Alder Street at MLK Boulevard) and the opening of SE Alder Street is expected by mid to late March.

The next phase of work at Outfall 44A (N. River and Randolph streets) was to launch the MTBM for its drive to the River Street Shaft beginning in February. The MTBM should reach its destination in late April or early May.

At Outfall 46 (N. River Street at AshGrove Cement), restoration of this site was under way. Preparation for paving was continuing, with landscaping to follow in February.